Description of an epizootic and persistence of Streptococcus equi infections in horses.

The research investigates the prevalence and persistence of Streptococcus equi infections in different age groups of horses, identifying that 60.8% of 51 sick horses tested positive for the infection. It also highlighted that 19.4% of infected horses remained carriers of the infectious bacteria even after their symptoms disappeared.

Investigation of Streptococcus equi Infections in Horses

• The researchers conducted an in-depth study to define age-specific attack rates of Streptococcus equi infections in horses. This bacterium typically affects the upper respiratory tract and lymph nodes of horses, resulting in a condition commonly known as ‘strangles’.
• The results showed varying rates of infection across different age groups: 17.6% for broodmares, 47.5% for 1-year-old horses, and 37.5% for foals. It indicates that younger horses seem to be more susceptible to the infection.
• Streptococcus equi was isolated from various samples including nasal swabs, pharyngeal samples, or lymph node specimens. The bacterium was found in 31 out of the 51 sick horses, translating to 60.8% of the cases.

Identifying the Index Case

• The first case, termed as the ‘index case’, was associated with a male 1-year-old horse that had been transported from Kentucky to a farm identified as “farm A”. This index case was instrumental in tracking the spread of the infection and understanding the process of transmission.

Shedding of Streptococcus equi Post-Infection

• A significant finding of the research was that 6 out of the 31 strangles-infected horses (or 19.4%) remained as carriers or ‘shedders’ of Streptococcus equi even after clinical signs of the disease had ended. This implies the potential for re-infection or cross-infection in horse populations even after recovery.
• None of the horses that were exposed to the infected animals but did not develop the disease turned out to be shedders of S. equi. This points towards the need for effective isolation and management strategies for infected animals, even post-recovery, in order to prevent further spread of the disease.